The present invention relates to casing structure of a transmitter of a tire condition monitoring apparatus. More particularly, the present invention pertains to casing structure of a transmitter for a wireless tire condition monitoring apparatus that permits a driver in a vehicle passenger compartment to check conditions of tires, such as the air pressure.
Wireless tire condition monitoring apparatuses that allow a driver in a vehicle passenger compartment to check the conditions of vehicle tires have been proposed. The apparatus includes transmitters and a receiver. Each transmitter is located in the wheel of one of the tires and the receiver is located in the body frame of the vehicle. Each transmitter detects the tire conditions, such as air pressure and the temperature of the associated tire, and wirelessly transmits the detected information. The receiver receives data wirelessly transmitted by the transmitters with a reception antenna and displays the conditions of the tires, for example, on a display located in front of the driver's seat. Each transmitter is formed by electronic elements such as a pressure sensor and a transmission antenna, which are mounted on a substrate. The substrate on which the electronic elements are mounted is accommodated in a casing. The casing includes a valve stem through which air flows when inflating the associated tire. Each valve stem is mounted to a mounting hole of the associated wheel with a valve nut. At this time, the casing is in contact with a rim (drop center) of the wheel (Japanese Laid-Open Patent Publication No. 2001-174357).
However, the size of the wheels varies depending on the type of the vehicle. For example, 12–15 inch wheels are mainly mounted on light cars. On passenger cars, 14–18 inch wheels are mainly mounted. On busses and trucks, 17.5 inch, 19.5 inch, and 22.5 inch wheels are mainly mounted. Therefore, the curvature of wheels differs depending on the size of the wheels. Thus, legs of the casing need to have the length corresponding to the curvature of the wheel to mount the casing to the wheel such that the legs of the casing abut against the wheel rim. Furthermore, if the casing is mounted to the wheel such that the legs of the casing abut against the wheel rim, the casing is prevented from rotating with the rotation of the valve nut when mounting the valve stem to the mounting hole of the wheel with the valve nut. However, manufacturing the casing such that the legs of the casing correspond to the size of the wheel is inefficient.